Heretofore, an interlayer insulating film is formed for the purpose of insulation between wiring layers in a multilayer wiring structure on a semiconductor substrate or the like.
In the above-mentioned multilayer wiring structure, a problem of signal delay due to a parasitic capacitance between wirings and a wiring resistance has becomes unavoidable. It is therefore required to use an interlayer insulating film having a low dielectric constant (Low-k).
In a semiconductor device according to the related art, an interlayer insulating film structure is formed on a semiconductor substrate provided with a number of semiconductor elements. The interlayer insulating film structure comprises a barrier cap layer of silicon carbide (SiC) or the like, a carbon-containing silicon oxide (SiOC) film formed on the barrier cap layer, a via hole formed in the SiOC film, a PAR (low-dielectric-constant silicon (Si)) layer, a trench formed in the PAR layer, and a hard mask of silicon oxide (SiO2) covering them. A metal such as copper (Cu) is filled in the via hole to form an electrode or a wiring. At an upper end of the via hole, Cu or the like is filled in the trench to form a wiring.
As the above-mentioned interlayer insulating film, attention has been paid to a fluorocarbon film (hereinafter referred to as a CFx film) which has a dielectric constant k as very low as about 2.5 so that the parasitic capacitance between wirings can be reduced. However, the CFx film is very weak against water and poor in adhesion. Therefore, the CFx film is formed on a base layer or an underlayer, such as a silicon carbonitride (SiCN) layer, a silicon nitride (SiN) layer, an SiO2 layer, or a SiC layer.
Heretofore, the CFx film is formed, for example, by the use of a plasma processing apparatus using a plasma-generating gas, such as He, Ne, Ar, Xe, or Kr, and using a fluorocarbon gas (hereinafter referred to as a CFx gas, e.g. a C5F8 gas), as described in Patent Document 1. In Patent Document 1, in order to adjust an electron density of generated plasma, N2, H2, or NH2 is used as a diluent gas in combination with the rare gas. Consequently, good adhesion and an excellent film shape are obtained.
[Patent Document 1] JP-A-2002-220668